Hydraulic valve and system

ABSTRACT

This invention relates to hydraulic control systems of the amplifier and servo valve type and to an improved valve advantageously employed in such systems. The specification discloses a hydraulic wheatstone bridge all four legs of which includes means for varying the pressure drop in that leg including a fluid nozzle in two of the legs flow from which is altered by a movable vane actuated electromagnetically. The vane is mechanically connected to the output member the position of which is also controlled by hydraulic pressure to create a control system with feedback.

United States Patent Inventor Appl. No. 4 Filed Patented Assignee Robert J. Bernstein Garden Grove, Calif. 769,49 1

Oct. 22, 1968 Jan. 12, 1971 A. B. G. Hydraulics, Inc. Garden Grove, Calif.

a corporation of California HYDRAULIC VALVE AND SYSTEM 8 Claims, 10 Drawing Figs.

[1.8. CI. 137/85, 137/625.64, 137/625.62, l37 /625.63 Int. Cl. ..Fl5b 13/02, Fl 5b 5/00 Field ofSearch l37/625.6l,

[ 56] References Cited UNITED STATES PATENTS 3,233,623 2/1966 Gray 137/625.62X 3.339.572 9/1967 Gordon l37/625.64X

Primary Examiner-Alan Cohan Attorney-Nienow & F rater ABSTRACT: This invention relates to hydraulic control systems of the amplifier and servo valve type and to an improved valve advantageously employed in such systems. The specification discloses a hydraulic Wheatstone bridge all four legs of which includes means for varying the pressure drop in that leg including a fluid nozzle in two of the legs flow from which is altered by a movable vane actuated electromagnetically. The vane is mechanically connected to the output member the position of which is also controlled by hydraulic pressure to create a control system with feedback.

HYDRAULIC VALVE AND SYSTEM and to an improved preamplifier and servovalve system which advantageously employs that valve. It is an object of the invention to provide an improved servovalve whose configuration is such that the dynamic and static forces acting on the valve are balanced despite dimensional variation in manufacture. Another object of the invention is to provide an improved valve whose configuration makes it convenient to incorporate the valve in a variety of hydraulic circuit configurations ineluding configurations providing direct mechanical control of the valve with and without mechanical and/or hydraulic feedback, hydraulic pressure control with and without mechanical and/or hydraulic feedback, combinations of mechanical and hydraulic pressure control with and without mechanical and hydraulic feedback, hydraulic pressure control with mechanical feedback and mechanical pressure control with hydraulic feedback.

It is also an object of the invention to'provide improved systems of this kind and, in particular, to provide improved systems including preamplifiers of hydraulic power. In this connection, it is an object of the invention to provide improved hydraulic circuits of bridge configuration which lend themselves to feedback control. his an object of the invention to provide an improved Wheatstone bridge, hydraulic circuit in which control is exercised in all four legs of the bridge and which advantageously employs the improved valve envisioned in the invention. I

Another object of the invention is to'provide a hydraulic valve and system employing that valve which will operate successfully and reliably at high pressure and large flowswhile providing rapid and accurate response to input control signals.

These and other objects and advantages of the invention which will hereinafter appear are realized in part by the provision of a hydraulic bridge circuit comprising a pair of parallel flow paths from a pressure inlet to a drain outlet, each of the paths including, in series, two means for altering pressure along the path; an output element responsive to alter its position as a function of pressure differential measured from a point in one of the paths intermediate said means for altering pressure in that path to a point in the other of the paths between its means for altering pressure along the path; by the inclusion of means responsive to a condition for changing the effectiveness of said means for altering pressure sufficiently to result in movement of the output element; and by the provision of means responsive to the condition for developing a force and applying that force to the output element. Certain of the foregoing objects and advantages of the invention are realized by other combinations of the elements envisioned within and comprising the invention. J

The system selected for illustration in the drawing incorporates the elements and features of the invention, it being understood that the various elements and structures shown are capable of embodiment in other forms and that the system shown may be otherwise structured and that other system arrangements areenvisioned and provided by the invention.

In the drawings:

FIG. 1 is an isometric view of an assembled servovalve and preamplifier assembly embodying the invention;

FIG. 2 is an exploded view of the several sections of the assembly of FIG. 1, the uppermost section being shown frag-' merited;

FIG. 3 is a cross-sectional view taken on line 3-3 of FIG. 1

on the vertical center plane of that assembly;

FIG. 6 is a view in horizontal cross section of a portion of the section illustrated in FIG. 5. takenon line 6-6 of FIG. 5;

FIG. 7 is a schematic drawing of the servovalve. its ports and passageways. illustrating the pathof fluid through the valve;

FIG. 8 is a schematic drawing of the system incorporated in the apparatus of FIG. 1;

FIG. 9 is a view in vertical cross section through the flow distributor of the valve taken on line 9-9 of FIG. 2; and

FIG. 10 is a view in horizontal cross section of the rotor of FIG. 9 together with a fragment of the valve casing in which the rotor is housed, taken on line 10-10 of FIG. 9.

Referring to FIG. 1 of the drawing, there is shown a valve and preamplifier assembly which includes four sections arranged, sandwichlike, one above the other. The assembly 10 is held together by four bolts 12 which extend through the upper cover section 13, the servocontr ol section 14, the servovalve section 15 to a threaded connection with the base section 16. The unit shown in FIG. 1 is intended for use with a source of hydraulic fluid under pressure, a fluid return or drain. and a hydraulic unit which is to be supplied with hydraulic fluid in accordance with operation of the servovalve. An electrical connector 17, by which electrical input signals are supplied to the unit, is visible in FIG. 1 at one side of the cover section 13. Two input ports for hydraulic control fluid are provided at opposite sides of the amplifier section 14 of the unit. One of these ports is visible in FIG. '1 and is designated by the reference numeral 18. All of the remaining ports open at the bottom, in FIG. 1, of the base section 16. Mounting holes 19 are provided in the base so that the unit may be mounted by bolts extending through these holes.

The general organization of this embodiment of the invention can be understood by reference to FIG. 2. The servovalve section 15 is provided with an opening 20 which extends vertically through the center of that section. The opening 20 'accommodates a rotor 21 which is generally cylindrical in form and is free to oscillate relative to the valve body or casing 22. The rotor is provided with diametric extensions which operate as vanes in cooperation with flow dividers which extend into the opening 20 whereby the rotor 21 is caused to oscillate with respect to the body 22 as a result of hydraulic pressure applied between the vanes and the flow dividers. The rotor'is' provided with a number of fiow openings, as best illustrated in FIG. 9, which cooperate with several flowpassageways and ports, the arrangement of which is illustrated in FIGS. 5, 6 and "land the function of which is illustrated in FIGS. 7 and I0. Essentially section 15 directs fluid from a pressurized source to one or the other of two outlet ports in variable fdegree depending upon the direction and amount of rotation of the rotor 21.

The function of the base section 16 is to complete the several passageways of section 15 and to provide means for FIG. 4 is a view in vertical sectionof one of the sections of the assembly taken on line 4-4 of FIG. 2;

FIG. 5 is a view in central vertical section of one section of the assembly of FIG. 1 taken on line 5-5 of FIG. 2;

connecting those passageways to the source of pressurized fluid, to the two output lines, and to a drain. The arrange t of its several passageways is illustrated in the 'lin FIG. 2 and in the sectional view of the section in FIG.'3.'

The amplifier section '14 houses a pair of "nozzles, passageways and flow control em elements for controlling flow to the nozzles and a vane which is interposed b een the nozzles and which is actuated by electromagnetic apparatus mounted upon the upper face, in these-drawings, oftlidbody or casing 23 of section 14. A side view of the vane showing its relationship tb'the nozzles and that it has connection -tothe rotor 2lis shown in FIG. 3. The relationship of the noulesto one another and to the vane is shown in FIG. 4. The upper section 13 has a cavity 24 formed in its-lower face whichthe electromagnetic actuating apparatus is housed when the unit is assembled. The servosection 14 includes passagewayswhich cooperate with those of the valve section 15 'perrnittingintroduction of control fluid to this section and the removal of spent fluid to the drain.

Aswill be apparent in FIG. 7 when considered in connection with FIGS. 5, 6, 9. and 10, the fluid whose fl owi s controlled by the valve flows along parallel flow paths to" the valve. Flow is controlled both at the point of entrance to the valve and at the point of exit from the valve so that the valve comprises four sections, each of which has one inlet and alternative outlets or alternative inlets and one outlet. These features of the valve are important in relation to the objective of providing a balance, sensitive, and accurately responsive valve and system. Nonetheless, it is possible to understand the basic operation of the system without need to consider the multiple flow paths and control ports. Accordingly, in the interest of clarity and ease of understanding, the servovalve has been depicted in the schematic drawing of FIG. 8 as a slide mechanism capable of reciprocal motion, corresponding to the oscillatory motion of rotor 21, within an elongate chamber 26. The chamber is formed in a casing 27 through which three flow passageways are formed. These three passages, which are designated by the reference numerals 28, 29 and respectively, communicate with the interior of the casing 27 at chamber 26. The flow distributor slide 25 is provided with a cutout 31 into which fluid from a pressurized source, P may flow through inlet passageway 29. When the slide 25 occupies the central position, it is shown to have in FIG. 8, fluid is precluded from flowing from cutout 31 to either of the output passageways 28 or 30. However, upon movement of the slide 25 to the left, in FIG. 8, in any degree fluid will be permitted to flow from the source through passageway 29 and cutout 31 and out the passageway 28. Fluid emerging at the passageway 28 is designated Pl conventionally and it is so designed in FIG. 8. The amount of fluid that flows out passageway 28 depends upon the degree of leftward movement of the slide 25. Conversely, if the slide 25 is moved to the right then the cutout 31 will uncover the exit port 30 in proportion to the degree of rightward movement of the slide permitting the flow of fluid from inlet passage 29 through the cutout 31 and through passage 30. Fluid emerging from the passage 30 is here designated, and conventionally so, by the symbol P It will be apparent that member 25, by its movement, controls the amount and direction of fluid flow through the flow paths 28, 29 and 30. These passageways are ordinarily connected to some fluid powered apparatus such for example as a double acting actuator piston. However, the slide 25 is the output element for the system shown in FIG. 8 and the output variable is the position of the slide. Pressurized fluid from a source P,, is introduced into the casing 27 as passageway 32 from whence it flows to the chamber 33 at the left of slide 25 and to chamber 34 at the right of the slide. The slide has dimensions complementing the dimensions of the cavity 26 so that it divides the cavity into the two chambers 33 and 34 whereby no communication other than small, incidental leakage is provided within the cavity 26 between the two chambers. Fluid may flow from chamber 33 by a passageway 35 to a nozzle 36 which discharges into a space 37. Fluid from chamber 34 may flow by a passage 38 to a nozzle 39 from which it flows into the space 37. An outlet passage 40 connects from the space 37 to a drain as indicated by the arrow marked D. A movable vane 41 is mounted so that its end extends between the two nozzles. In the absence of force applied to move the vane from that position, it normally extends between the two nozzles 36 and 39 so that the impedance to flow from nozzle 36 equals the impedance to flow from nozzle 39. In this circumstance, the impedance to flow from source P, through chamber 33, line 35. nozzle 36 to space 37 equals the impedance through flow from the source to chamber 34, through passage 38 and nozzle 39 to the space 37. In this case the pressure in chambers 33 and 34 are equal and the slide will occupy the position it is shown to have in FIG. 8.

Thus far described, the fluid system which derives its fluid from source P serves to center the piston or slide 25 in the position shown. If an electrical current is applied to the electromagnet 42 the vane 41 will be deflected in proportion to the magnetic field developed by the ele'ctromagnet. Movement of the vane is coupled to the slide 25 by a pin 43 which interconnects them through a resilient connection comprising the centering spring set 143. Depending upon the direction and degree of this movement, flow will be directed from the passageway 29 to one of the other of the passageways 28 and 30. But such movement will be opposed by the fluid in chamber 33 or chamber 34 unless. or until, pressure in those chambers is relieved. Let it be supposed that electromagnet 42 is energized in a direction tending to move the lower end of vane 41 and slide 25 to the left. Such movement is permitted because the fluid in chamber 33 is forced from that chamber through conduit 35 and the nozzle 36 at an increased rate because the vane has moved away from the end of nozzle 36. This reduces the impedance to flow from the nozzle and permits greater flow. As the piston or slide 25 moves to the left it tends to close the opening 44 by which fluid flows from passageway 32 into the chamber 33. The leftward movement of slide 25 tends to open the port 45 by which fluid flows from line 32 to chamber 34 thus tending to increase the pressure in chamber 34. That increased pressure results in an increased pressure in line 38 and in nozzle 39. Accordingly, the fluid emerges from the nozzle 39 with greater force tending to oppose the leftward motion of the vane which initiated the action. The effect of these several actions and reactions is that the output member, here the slide 25, has its position altered in response to a force mechanically applied to the output member in response to the state of some condition, here the magnitude of current flow in the electromagnet, and that motion is opposed hydraulically in a feedback system which develops a hydraulic pressure across the ends of the output member. The output member motion ceases when the mechanical input force is matched by the pressure differential across the chambers 33 and 34.

Examination of FIG. 8 shows that the hydraulic circuit forms a Wheatstone bridge comprising four legs each of which includes a means for producing a pressure drop. Input power to the bridge in the form of a hydraulic pressure differential is applied across one pair of the opposite corners of that bridge. The bridge output is taken across the other opposite corners of the bridge in the form of displacement of the output member as incident to the pressure differential across those opposite corners. The hydraulic force across theoutput member, and thus its displacement, may be altered by altering the pressure drop at any one of the legs. A number of means are available for altering the pressure drop in one or more of the legs. Examples of structures by which a pressure drop may be altered are variable flow restrictors, variable leak openings and pressure pumps. In FIG. 8, and in the apparatus of F IG. 1. variable flow restriction is employed in all four legs of the bridge. The bridge is traced in the following manner. Input power is applied in the form of pressure differential from input P at input passageway 32 to output drain D at output passageway 40. There are two flow paths for fluid from the input to the output. One of these paths is traced from input passageway 32 through flow restriction 44, which is variable with displacement of the output element; through chamber 33 and conduit 35; through flow restriction or nozzle 36 the restriction of which is variable with movement of vane 41; discharge chamber 37; and thence to output line 40. The variable restriction 44 constitutes one leg of the bridge in this passageway and the other leg is formed by the orifice or variable flow restriction 36. The chamber 33 constitutes one corner of the bridge. The other flow path is traced from input line 32 through the flow restriction 45, which is variable by displacement of the output member; through chamber 34 and line 38; through the variable flow restriction comprised of the nonle 39 and the movable vane 41; to the output chamber 37 and then to the output line 40. The variable orifice 45 constitutes a third leg of the bridge and the nozzle 39 and vane 41 comprise the fourth leg of the bridge. The chamber 34, which occurs in the flow path intermediate these two variable restrictions, constitutes another corner" of the bridge. Thus. the input line 32 and output line 40 occur at one pair of opposite comers of the bridge and the chambers 33 and 34 occur at the other opposite corners of the bridge. Output of the bridge is measured as pressure differential across the chambers 33 and 34 or as the displacement of the output member as a result of this pressure differential, it being understoodthat movement of the output member isopposed by some force which here is the vane 41 to which the member is connected, in this embodiment through an elastic connection afforded byspring set 143.

It is apparent from this description that the displacement of the output member can be controlled by alteration of the pressure drop in one or more of the legs of the bridge. This can be accomplished in the circuit of FIG. 8 in a number of ways as, for example, by varying the pressure applied to one or more of the variable restrictions. Means are included in this circuit for doing just that. A'variable restriction in the form of a valve 50 controls the application of fluid pressure from a pressure con.- trol source P to the nozzle 39 anda Similarrestriction in the form of a valve, 51 controls the application of pressure from a control source P to the nozzle 36.1f the valves 50 and 51 are open so that pressure is applied to theno zzles 39 and 36, the pressures? and P, will .alter the flow from the source P through the two flow paths. The pressuredrop across chants bers 33 and 34 will vary as a function of the ratio of the pressures P and P resulting in a corresponding displacement of the output member.-If the pin 43 is omitted so that there is no connection between the vane 41 and the output member, the system will include no feedback but'if the pin is in included, so that the mechanical connection is completed, then the movement of the vane resulting from the differential in flow rate emanating from the nozzle 39 and 36 will result in a feedback movement of the output member. v

At this point attention is invited briefly to FIG. 3 at the upperend of the rotor 21 which is mounted for rotation (rotational oscillation) in section 15. Two holes aredrilled into the top of the rotor. One is to the left and-"the other is to the right of the-axis of rotor rotation. A pin 52 isconnected at its upper end to the vane 53. At its lower end the pin is disposed in the rightmost of the two rotor holes. The pin being connected in the right hand opening results in counterclockwise rotation of the rotor when the vane 52 is moved in the direction toward the page in the drawing but rotor rotation would be clockwise in response to such movement of the vane if the pin were connected in the leftmost rotor hole instead-Consequently, the

feedback may bechanged from negative to positive by chang-. ing the point of connection to the rotor to the opposite side of the rotation of its rotationalaxis. 1 a

Returning to FlG. 8, whenthe valves and 51 are closed, the hydraulic system described above is in fact the feedback circuit of the total system. when the electromagnet 42 is energized and when vane 41 is connected by pin 43 to the output member, then the mechanical input applied by the vane to the output member is the primary input of the system and this is the mode. of operation with which the description of FIG. 8 was begun. 7

In another mode of operation of this system the inlet pres? sure P is made zero relative to the discharge pressure. Con! trol is exercised by opening valves 5() and 51 and varying the ratio of the control pressures P and P ..Variation of this ratio will result in a differing force at the opposite sides of the vane. As an incident to this differing force the vane will move thereby moving the output member 25. This control can be supplemented by energizing the electromagnet 42.

Summarizing, whether its elements have the form shown oranother equivalent form, the system of FIG, 8. can be operated as a system whose primary input to the output member is a nonmechanical force which is opposed by a hydraulic dif-v ferential pressure feedbacksystem. Alternatively, it can be operated as a system in which control of the output member is had by the application of hydraulic differential pressure and in which feedback control is exercised'mechanically. By omission of the pin 43 and by reducing the pressureP to the pressure of the discharge drain, the mechanical and hydraulic feedback may be eliminated. Also, the output member movement and displacement may be controlled jointly by mechani-. cal or electromechanical and hydraulic means.

One other mode of operation is possible. If the hydraulic feedback circuit is made operative by applying to input line 32 gization of the electromagnet 42. On the other hand the electromagnet can be energized in uniform degree to oppose motion of the vane with a predetermined bias whereby to adjust the gain of the preamplifier section of the system.

While these various modes of a operation are available as operational features of the system provided by the invention, normally only one mode would be employed in a given system. However, it is an attributes of the valve that its symmetry tends to makethevalve sensitive to control while minimizing valvesticking and backlash hysteresis and other ills common to valves of this type. These advantages are provided by a symmetryin the valve construction. The parts and passageways of the-unit are arranged so that the several modes of operation above described 2 are possible by opening and closing passageways and valves and by the use or nonuse of the mechanical connectionbetween the vane and rotor without sacrificing that symmetry. As illustrated in section 15 of H6. 3 and in FIG. 5, the flowdistributing rotor2l is disposed in a cavity of the casing body 23 that extends entirely through the body at its center. The cavity is divided into two cavities each of which contains a portion of the rotary flow distributor 21. The cavity is formed as a longitudinal bore having one diameter over diametric circular segments less than the whole and having a smaller diameter over the remaining diametric segments. The rotor 21 comprises a generally cylindrical member having a diameter substantially equal to the diameter of the first mentioned circular segments of the cavity over diametric segments less than the whole and a diameter less than the larger diameter diametric segments of the bore. More particularly, the rotor has a diameter substantially equal to the diameter of the smaller diameter segments of the bore over a circulatsegment less than the whole and greater than the smaller diameter diametric segments of the bore. 'The larger diameter diametric segments of the rotor serve as vanes which are mounted for oscillation in the larger diameter diametric segments of the bore. That portion of the casing body 23 which occupies the space between the smaller diameter diametric segments of the bore and the diameter of the larger segments of the bore comprises two flow dividers one extending longitudinally of the rotor on opposite sides of the rotor. One rotor vane is designated by the reference numeral and the other is designated 61. The flow dividers are numbered 62 and 63, respectively. This relationship and the fact that the rotor-is free to oscillate within thevalve cavity or bore is best shown in FIG. 10. The result is that the cavity is divided into two portions one an elongate opening arcuate in cross section whose ends aredefined by the flow dividers 62 and 63 and in which the vaneportion 60 of the rotor is disposed. The other section of the cavity is also elongated, arcuate in cross section and it has the vane portion 61 of the rotor disposed in it. The cavity att'he right is divided by the vane 60 into two chambers 64 and 65. The vane 61 divides the other half of the cavity into two chambers designated 66 and 67'. Fluid pressure in cavities and 67 tend to force counterclockwise rotation, in FIG. 10, of. therotor 21 relative to the casing body 23.'The two cavities 64 and 6 7 are interconnected by a passageway shown dotted and designated by the numeral 68. Another passage shown dotted and designated by the numeral 69 is. bored through the rotor on another diameter and intersects with the passage 68.

l-lydraulic fluid is supplied to the cavities 64 and 67 through by an inlet port 73 formed in the casing body 23 and opening at the inner wall of the rotor cavity such that fluid is supplied to the cavities 65 and 66 in any rotational position of the rotor at a rate which depends upon the degree of rotor rotation. If the pressure in cavities 65 and 66 exceeds the pressure in cavities 64 and 67 the rotor will rotate counterclockwise whereas if the pressure in cavities 64 and 67 is greater than that in the other two, the rotor will turn clockwise. This arrangement. in which actuating pressure is applied at spaced points around the entire diameter of the rotor, results in a balance of forces which contributes to ease of rotor operation despite the fact that unbalanced forces are required to make the rotor turn. The fact that the input passageways 69 and 72 extend to diametric points of the piston contributes to the force balance that keeps the rotor centered within its cavity.

The inlet ports 70 and 73 are connected to the fluid pressure inlet line. The supply pressure inlet connection is located at the bottom center of the base section 16 and is shown in dotted lines in FIG. 3 and in FIG. 2 where it is identified by the reference numeral 74. Flow is divided between two laterally extending passageways designated 75 in FIG. 2. These passageways connect with respective ones of vertically directed passageways which open at the upper face of the base section 16 at openings 76 and 77. These passageways communicate with passageways 78 and 79, respectively, which are formed in the lower face of the casing body 23. A passageway 80 connects the opening 78 with the passageway 70 and a passageway 81 connects the opening 79 with passageway 73. These several passageways are shown in dotted lines in FIG. 6. The point at which passageways 70 and 73 open to the interior of the cavity and at which they are closed in variable degree by rotation of the rotor correspond to the variable flow restrictions 44 and 45 of FIG. 8. Chambers 64 and 67 correspond to chamber 33 of FIG. 8 and chambers 66 and 65 correspond to chamber 34 of FIG. 8. Rotor control fluid leaves these chambers by a pair of passageways 82 and 83 which communicate, at their lower ends, with chambers 65 and 67, respectively, of the casing body 23. These passageways communicate with lateral flow paths 84 and 85, respectively, which are-bored laterally through the amplifier section 14 of the unit. The two passageways 84 and 85 are bored on a common axis and they open to an elongate slot formed in the lower face of section 14 with its sides parallel and equidistant from a vertical center plane through the unit in the direction so that it bisects the flow dividers 62 and 63 of the casing body section 23 below. The slot is milled out to a width less than the width of the flow dividers. Thus, the slot which is identified by the numeral 86 in FIG. 2 and one of whose walls is designated by the numeral 87 in FIG. 3. is sufficiently narrow so that flow from the cavity 65 is confined to the passageway 82 and flow from cavity 67 is confined to passageway 83. The slot is sufficiently long so that it extends over drain ports 88 and 89 of the section and drain ports 90 and 91 of the base section 16. A nozzle 92 is fitted to the inner end of the passageway 85 and another nozzle 93 is fitted at the inner end of the passageway 84. Fluid entering passage 84 via the passageway 82 is discharged to the slot 86 through nozzle 93. Similarly, fluid flowing upwardly in the chamber 67 passes by passageway 83 and passageway 85 to the nozzle 92 from whence it is discharged into the slot 86. An opening from the upper face of section 14 extends through to the slot in the central region of the section 14. The shank of the L-shaped vane 53 extends through that opening. The lower part of the vane extends lengthwise of the slot midway, in quiescent condition, between the two nozzles 92 and 93. The shank of the vane 53 extends upwardly through the energizing coil 94 of a C-magnet 95 to which the upper end of the vane 53 is fixed. The magnet and coil are secured to the upper face of the section 14 by any convenient means, now shown, so that it is free to cantilever toward either of the nozzles and away from the other. Means are provided for centering the vane. This means comprises a pair of springs which act on opposite sides of the vane. The springs are indicated schematically in FIG. 8 and one spring is shown in dotted lines in FIG. 3

where it is designated by the reference numeral 96. The nozzles 92 and 93 correspond to the nozzles 39 and 36 of FIG. 8. and the vane 53 corresponds to the vane 41 of FIG. 8. The electromagnetic actuator 42 of FIG. 8 corresponds to the magnet and coil assembly and 94. As in the embodiment illustrated schematically in FIG. 8. the embodiment depicted in the remainder of the FIGS. includes passageways 84 and 85 by which an external control pressure can be applied to the nozzles. In this case, however, those passageways are not provided with control valves, but instead are closed by a pair of plugs 100. The fact that the vane 53 is connected to the rotor distributor 21 by a pin 52 has already been described.

The function of the control system, including the preamplifler and the feedback control system, is to rotate the rotary distributor 21 so that fluid from a source will be directed to either one of a pair of outlet ports in a degree corresponding to the degree of rotation of the rotor. A schematic of the hydraulic system thus controlled is illustrated in FIG. 7 where the upper and lower portions of the rotary distributor and the surrounding portions of the valve casing 23 are shown separately. The upper portion of the rotor is shown in the upper rotor drawing in FIG. 7 and the lower portion of the rotor 21 is shown in the lower rotor section of FIG. 7. Fluid from a pressurized source is introduced into inlet ports 101 and 102 opening to opposite sides of the rotor cavity at a vertical level corresponding to the level of a pair of diametric cutouts 103 and 104 formed in the exterior wall of the vane portions of the rotor. The edges of the cutouts extend substantially exactly to but do not overlap a pair of exit ports I05 and 106 on opposite sides of the inlet port 101. A pair of ports I07 and 108 open to the rotor cavity on opposite sides of the inlet port 102 and are spaced substantially exactly the width of the cutout 104. Rotation of the rotor clockwise in FIG. -3 will rotate the cutout 103 such that flow is permitted from the inlet 101 to the outlet and from inlet 102 through the cutout 104 to the outlet port 108. Counterclocltwise rotation from the center position, which the rotor occupies in FIG. 7, connects the inlet 101 to outlet 106. The quantity of fluid that is permitted to flow depends upon the supply pressure and the degree of rotation of the rotor.

The upper section of the rotor is provided with two outlet ports 110 and 111. There are two inlet ports I12 and 113 on opposite sides of outlet port 110 and there are two inlet ports 114 and 115 on opposite sides of the outlet port 111. The rotor is provided with a pair of cutouts. Cutout 116 is formed opposite outlet 110 and cutout 117 is formed opposite outlet 111. The cutouts extends to but do not overlap the edges of ports 112 and 113 in the case of cutout I16 and of ports I14 and 115 in the case of cutout 117. If the rotor is moved clockwise the cutout 116 will underlie the outlet 110 and a portion of inlet 112 whereby fluid flow from the inlet 112 through the outlet passage 110 is permitted in proportion to the degree of rotor rotation. Similarly, fluid entering at port 115 may pass through cutout 117 to the outlet 111. Outlet 106 is connected to inlet 112, outlet 105 is connected to inlet 113. Outlet 107 is connected to inlet 115 and outlet 108 is connected to inlet 114. The fluid inlet passageways 101 and 102 communicate with fluid inlet openings 79 and 78, respectively, as best shown in FIG. 5. Also, in FIG. 5. it is seen that outlet passageway 110 connects with an outlet opening 120 and outlet passageway 111 connects with an outlet opening 121. Openings 120 and 121 connect with corresponding openings 122 and 123, which are shown dotted in section 14 of FIG. 2. from whence the fluid is communicated by lateral passageways to the slot 86 from which it is free to flow to the outlet passages 88 and 89 of section 15 and thence to passages 90 and 91 of the base section. The output lines P1 and P2 are formed by flow paths and 131 in the base section 16 and by flow paths 132 and 133 in the valve section 15. The passageways 132 and 133 are connected to the network of internal passageways indicated by dotted lines in section 15 of FIG. 2 and FIG. 3. Part of that network is visible in FIG. 6 where it is seen to be symmetrical in the sense that the flow path for fluid throughhothof the pathways is forrne't'iof individual passageways having the same length, same number of turns and which are turned at the same angle. The arrangement is shown functionally in FIG. 7 f' 7 Although I have shown and described certain specific embodiments of my invention, I am fullyaware that many modifications thereof are possible. My invention therefore is not to be restrictedeitcept insofaras isnece'ssitated by the prior art and by the spirit of the appended claims.

lclaimzn l i I 1. In combination: I H a fluid inlet for connection to asource of fluid under pressureand a fluid drain, two paths in parallel for conducting fluid from said inlet to the drain, each of the paths including first and second pressure drop means inseries for developing a fluid pressure drop in'their respective flow path as an incident tofluid flow therethrough; an output element responsive to alter its position as a functionof pressure differential measured from apoint in one of said paths between said first and second pressure drop means thereof to a point in the other of said paths between said f rst and second thereof; r 4 means responsive to a condition for changing the effectiveness of at least one of said pressure drop means relative to the others sufficiently to effect alteration of .saidpressure differential; and a g g l in which one ofthe pressure drop means in each of said flow paths comprises a flow/restrictor variable as a function of displacement of said .output element, the variation in the two flow restrictors being of opposite degree; and in which the other pressure drop means in each flow path comprises one'flow restrictor of a pair whichare variable in opposite degree in response to said condition. 2. The invention defined in claim 1, in which said last mentioned flow restrictors comprise: fluid nozzles, said means responsive to a condition for changing the effectiveness of one of the means for developing a pressure drop comprising a structure movable in response to said condition to impede fluid flow from said nozzles in variable degreesuch that move ment. to increase impedance toflow in one nozzle reduces the impedance to flow from the other.

3. The invention defined in claim 2, including means for varying flow from said nozzles independently of movement of said structure and independently of displacement of said output element.

4. in combination:

a fluid inlet for connection to a source of fluid under prespressure dlOp meanssure and a fluid drain, two paths in parallel for conducting fluid from said inlet to the drain, each of the paths including first and second pressure drop means in series for developing a fluid pressure drop in their respective flow path as an incident to fluid flow therethrough;

an output element responsive to alter 'itsposition as a function of pressure differential measured from a point in one of said paths between said first and second pressure drop means thereof to a point in first and other of said paths between said first and second pressure drop means thereof;

means responsive to a condition forchanging the effectiveness of at least one of said pressure drop means relative to the others sufficiently to differential; 1

means responsive to the magnitude of said condition for developing a force'additional to said pressure differential effect alteration of said pressure menu I means for developing an additional'force and for coupling that force to said output element being effective to couple said additional force to said output element to oppose the efiect imposed on said output element by said pressure differential; a casing defining a cavity m which the output element is disposed, the output element having dimensions to divide the cavity into a pair of fluid chambers and being movable in response ,topressure differential measured from one chamber to the other; one chamber having fluid commu. nication with said point in said one flow path and the other chamber having fluid communication with said point of the other flow path;

.said means responsive, to said condition for developing and applying an additional force comprising means for coupling to said output element mechanical forces tending to move the element relative to the casing in a directionto increase the volume of onechamber While decreasing the volume of the other; and

thepressure drop means in each of theflow paths comprising a variable flow restrictor, the degree of restriction of which is variable in response to movement of said output element such that the degree of restriction in the two restrictors varies oppositely, and in which the other pressure drop means in each flow. path comprises a variable flow restrictor, said means responsive to a condition for changing the effectiveness of at least one of said pressure drop means comprising means for varying the degree of restriction of said last mentioned flow restrictors in opposite degree.

5..The invention defined in claim 4, in which said last mentioned pair of flow restrictors comprise fluid nozzles and said means responsive to a condition for changing the effectiveness of those flow restrictors comprises a structure movable in response to said condition to impede flow from said nozzles in variable degree such that movement to increase impedance in flow from one nozzle reduces the impedance to flow from the other.

6. The invention defined in claim 5, in which said means responsive to said condition for coupling additional force to said output element comprises a mechanical connection from said structure to said output element.

7. The invention defined in claim 6, in which said output element comprises a rotary flow distributor in the form of an elongate cylinder having a pair of diametrically disposed vanes extending radially from the cylinder. said cavity comprising a cylindrical bore in which the rotor is disposed. the casing comprising a pair of flow dividers formed at diametric points of the cavity and extending radially inward toward one another. said rotor and its vanes having dimensions relative to the cavity and its flow dividers to divide the cavity into two cavities and each vane of the rotor dividing one of the cavities into two chambers such that each rotor has one cavity at its clockwise side and one cavity at its counterclockwise side, the two clockwise cavities being connected to said point in one of the flow paths and said counterclockwise' cavities being connected to said point in the other of said flow paths. 1

8. The invention defined in claim 7, in which connection to said counterclockwise cavities and connection to said clockwise cavities being made through ports in said casing and for coupling that additional force to said output eleopening one in each of said cavities, each vane of said rotor overlying a respectively associated one 'of said ports and being effective to open and close said port in variable degree as an incident to rotation of the rotor. 

1. In combination: a fluid inlet for connection to a source of fluid under pressure and a fluid drain, two paths in parallel for conducting fluid from said inlet to the drain, each of the paths including first and second pressure drop means in series for developing a fluid pressure drop in their respective flow path as an incident to fluid flow therethrough; an output element responsive to alter its position as a function of pressure differential measured from a point in one of said paths between said first and second pressure drop means thereof to a point in the other of said paths between said first and second pressure drop means thereof; means responsive to a condition for changing the effectiveness of at least one of said pressure drop means relative to the others sufficiently to effect alteration of said pressure differential; and in which one of the pressure drop means in each of said flow paths comprises a flow restrictor variable as a function of displacement of said output element, the variation in the two flow restrictors being of opposite degree; and in which the other pressure drop means in each flow path comprises one flow restrictor of a pair which are variable in opposite degree in response to said condition.
 2. The invention defined in claim 1, in which said last mentioned flow restrictors comprise fluid nozzles, said means responsive to a condition for changing the effectiveness of one of the means for developing a pressure drop comprising a structure movable in response to said condition to impede fluid flow from said nozzles in variable degree such that movement to increase impedance to flow in one nozzle reduces the impedance to flow from the other.
 3. The invention defined in claim 2, including means for varying flow from said nozzles independently of movement of said structure and independently of displacement of said output element.
 4. In combination: a fluid inlet for connection to a source of fluid under pressure and a fluid drain, two paths in parallel for conducting fluid from said inlet to the drain, each of the paths including first and second pressure drop means in series for developing a fluid pressure drop in their respective flow path as an incident to fluid flow therethrough; an output element responsive to alter its position as a function of pressure differential measured from a point in one of said paths between said first and second pressure drop means thereof to a point in first and other of said paths between said first and second pressure drop means thereof; means responsive to a condition for changing the effectiveness of at least one of said pressure drop means relative to the others sufficiently to effect alteration of said pressure differential; means responsive to the magnitude of said condition for developing a force additional to said pressure differential and for coupling that additional force to said output element; means for dEveloping an additional force and for coupling that force to said output element being effective to couple said additional force to said output element to oppose the effect imposed on said output element by said pressure differential; a casing defining a cavity in which the output element is disposed, the output element having dimensions to divide the cavity into a pair of fluid chambers and being movable in response to pressure differential measured from one chamber to the other; one chamber having fluid communication with said point in said one flow path and the other chamber having fluid communication with said point of the other flow path; said means responsive to said condition for developing and applying an additional force comprising means for coupling to said output element mechanical forces tending to move the element relative to the casing in a direction to increase the volume of one chamber while decreasing the volume of the other; and the pressure drop means in each of the flow paths comprising a variable flow restrictor, the degree of restriction of which is variable in response to movement of said output element such that the degree of restriction in the two restrictors varies oppositely, and in which the other pressure drop means in each flow path comprises a variable flow restrictor, said means responsive to a condition for changing the effectiveness of at least one of said pressure drop means comprising means for varying the degree of restriction of said last mentioned flow restrictors in opposite degree.
 5. The invention defined in claim 4, in which said last mentioned pair of flow restrictors comprise fluid nozzles and said means responsive to a condition for changing the effectiveness of those flow restrictors comprises a structure movable in response to said condition to impede flow from said nozzles in variable degree such that movement to increase impedance in flow from one nozzle reduces the impedance to flow from the other.
 6. The invention defined in claim 5, in which said means responsive to said condition for coupling additional force to said output element comprises a mechanical connection from said structure to said output element.
 7. The invention defined in claim 6, in which said output element comprises a rotary flow distributor in the form of an elongate cylinder having a pair of diametrically disposed vanes extending radially from the cylinder, said cavity comprising a cylindrical bore in which the rotor is disposed, the casing comprising a pair of flow dividers formed at diametric points of the cavity and extending radially inward toward one another, said rotor and its vanes having dimensions relative to the cavity and its flow dividers to divide the cavity into two cavities and each vane of the rotor dividing one of the cavities into two chambers such that each rotor has one cavity at its clockwise side and one cavity at its counterclockwise side, the two clockwise cavities being connected to said point in one of the flow paths and said counterclockwise cavities being connected to said point in the other of said flow paths.
 8. The invention defined in claim 7, in which connection to said counterclockwise cavities and connection to said clockwise cavities being made through ports in said casing opening one in each of said cavities, each vane of said rotor overlying a respectively associated one of said ports and being effective to open and close said port in variable degree as an incident to rotation of the rotor. 